There have been many processes proposed by which catalysts in a catalytic reactor can be activated, deactivated, heated, or cooled in situ in the catalyst beds. However, insofar as the inventors are aware, in all these cases, the plant must be operating either totally or partly in order to accomplish this. As a result, considerable time and production are thus lost by the plant in having to heat, activate or deactivate catalysts, particularly after a plant shutdown, since production cannot be made until these steps are taken. The scope of this problem can be appreciated, when it is considered that plant production may be worth in the neighborhood of several hundred thousand dollars or more per day. Further, many of these processing steps require two to three days to place the catalyst in proper condition for process use. Accordingly, by use of the process and of the apparatus of this invention, the catalyst can be prepared so as to be ready to go on stream immediately, thus conserving otherwise wasted time in placing the plant into production.